# -*- coding:utf-8 -*-
if __name__ == "__main__":
	x,y = map(int,raw_input().split())
	x2,y2 = map(int,raw_input().split())
	ans = max(x,y)
	if x != 0 and x2 != 0:
		if y != 0 and y2 != 0:
			if abs(x) == abs(y) and abs(x2) == abs(y2):
				if min(x,0) <= x2 and x2 <= max(x,0):
					ans += 1
	print ans